Known therapeutic heat transfer devices relieve aches, pains, tensions in mammals (warm-blooded creatures, such as humans), and reduce swelling, among other things; they also have cosmetic use for opening the pores of the skin, as in beauty treatments and dermatological uses. This is achieved by promoting blood circulation through the limbs against which the heat transfer device is applied.
The effects of localized thermal transfer to bodily parts with these known thermal transfer devices is well documented in the art. Such heat transfer devices include:
(a) the simple hot water-filled bag, or conversely, the ice pack filled with water ice; PA1 (b) electric blankets, which include insulated, multi-layered, flexible sheets, and a heat cell embedded within the sheets and generating continuous heat upon plugging the electric wire thereof in an electrical wall plug; PA1 (c) chemical steam packs, which generate heat upon unsealing the pack, thus enabling exothermic oxydation of the air-responsive, reactive chemical agent within the pack, for a period of about half an hour--they are used e.g. by alpine skiers inside their hand gloves; see for example U.S. Pat. No. 3,874,504 to Verakas; PA1 (d) mineral-filled heat pads, with a flexible envelope enclosing granular mineral material (usually sand or vulcanite); the pad is pre-heated in an oven before use, to enable slow diffusion of heat absorbed by the mineral crystals--see for example international patent application No PCT/EP90/00785 published on Nov. 29, 1990 in the name of Herbert Hans WAGNER; PA1 (e) gel-based thermal packs, with an envelope enclosing a gel-state material having a substantial water content associated with a liquid-absorbing core, this core including for example propylene glycol and formaldehyde (to extend the overall thermal range of the gel-state of the material before reaching freezing or boiling state)--see for example U.S. Pat. Nos. 4,488,552 issued Dec. 18, 1984 to Micropak manufacturing, inc., and 4,920,964 issued May 1, 1990 to Jack Frost Laboratories inc.; these thermal packs release stored heat slowly, after being pre-heated for a while in an oven, as with the mineral-filled heat pads, supra.
These prior art heat transfer devices, although effective, have a number of drawbacks. The electric blankets, for one, generate magnetic fields. Currently, there is considerable controversy as to whether or not long exposure of biological tissues to high levels of electromagnetic fields is linked to cancerous cell development. Extensive studies on the interaction of electric fields with living matter have brought concerns to the scientific community as to the health hazards associated with electric blankets. See for example the "CRC Handbook of biological effects of electromagnetic fields", Charles POLK editor, CRC Press, Boca Raton Fla. [1986].
Chemical steam packs are of the disposable type, i.e. they can be used only once. Their cost is accordingly high, relative to reusable heat transfer pads such as the mineral-filled pads and the gel pads. Moreover, the dosage of reactive agent inside the sealed pouch is critical in order not to overheat the pouch--indeed, some cases of bodily injuries have been reported a few years ago in the press, from skin exposure to such chemical steam packs due probably to an improperly measured amount (i.e. an amount greater than required) of reactive chemical agent in the pouch.
Gel type heat pads have a tendency to burst if the preheating period exceeds the recommended time period. The margin for error is very small, as is indeed candidly reported in the specification of the two above-noted gel-type U.S. patents. A burst pad becomes unreusable, and may further constitute a safety hazard. Moreover, gel pads tend to produce a so-called "moist" heat, which may not be desirable for everybody.
Mineral-based heat transfer pads have other drawbacks. Because of the extremely low water content of the granular mineral occur between the mineral granules as the flexible pad is repeatedly bent to fit around the various limb parts. Eventually, these granules accordingly become powdery (i.e., their granulometry progressively decreases), so that they may come to escape from the pad through the porous envelope wall. Moreover, mineral materials such as sand define granules each having relatively sharp external edges; such sharp edges are certainly uncomfortable to the skin as they indirectly come in contact therewith through the pad envelope wall. Also, because the granulometry of sand is quite small, it has been found by the three present joint inventors that the granular material pressure load-induced movement within the pad envelope and consequent distributive flow therein tend to easily generate empty grainless pockets within the pad envelope. In other words, instead of the granular material desirably spreading equally all along the enclosure of the pad envelope, the sand will tend to gather at the two opposite ends of the pad, under gravity-borne forces, while the intermediate section thereof (that is, the main pad section coming in contact with the body part to be soothed) will be substantially free from any heat-releasing core material (the two corresponding sections of the opposite main walls of the envelope will abut flatly against one another), an inefficiency.